1. Field of the Invention
The present invention relates to strain measurement apparatus, and more particularly to digitally switched resistive strain measurement apparatus in combination with a torque wrench.
2. Description of the Prior Art
The measurement of strain in portable tools has had extensive application. In particular, tools like torque wrenches have acquired increasing significance in assembly procedures of complex technological devices, where increasingly precise torque reading requirements are demanded. Furthermore, the assemblies of such complex structures, which typically increase in size with development of technology, require that tools like torque wrenches possess the characteristics of portability and reliability due to the repetitive use thereof. Thus, it is the increasingly complex structures that have created a need for an accurate, reliable and portable hand tool like a torque wrench. Heretofore, most prior art torque wrenches were either of the mechanical type depending on visual observation of mechanical strain or of the electrical type where the strain is converted to an electrical signal. In the latter type, large amounts of power were typically dissipated through the strain measuring elements during operation since most often the strain measuring circuits are powered upon manual actuation of a switch, such power being dissipated continuously whether the torque wrench is applying torque or whether it is unloaded. The requirement of portability in the torque wrench has therefore been largely complicated by such power loss since the power would either have to be directly supplied to the wrench or would have to be carried within the structure of the wrench in the form of a battery. This dissipation of power through resistive strain measuring elements of the typical prior art torque wrenches further complicate the accuracy of the reading since a thermal gradient can exist in these configurations resulting in errors in strain readout.